To simply and firmly support a corner ridge beam to a support base member of a building.

The structure has a diagonal 31 slantly arranged along a corner ridge 11 of the building. In the corner ridge beam 30, the lower end of the diagonal 31 is supported by the support base member (column 21, wall 22). The lower end of the diagonal 31 is cut off horizontally, a horizontal plate 32 is integrally formed in the horizontally cut off part. The horizontal plate 32 is made connectable to the support base member (column 21, wall 22).